Self-aligned, planar phase change memory elements and devices, systems employing the same and method of forming the same

ABSTRACT

Phase change memory elements, devices and systems using the same and methods of forming the same are disclosed. A memory element includes first and second electrodes, and a phase change material layer between the first and second electrodes. The phase change material layer has a first portion with a width less than a width of a second portion of the phase change material layer. The first electrode, second electrode and phase change material layer may be oriented at least partially along a same horizontal plane.

FIELD OF THE INVENTION

Embodiments of the invention relate to semiconductor devices and, inparticular, to phase change memory elements and methods of forming andusing the same.

BACKGROUND OF THE INVENTION

Non-volatile memories are useful elements of integrated circuits due totheir ability to maintain data absent a power supply. Phase changematerials have been investigated for use in non-volatile memory cells.Phase change memory elements include phase change materials, such aschalcogenide alloys, which are capable of stably transitioning betweenamorphous and crystalline phases. Each phase exhibits a particularresistance state and the resistance states distinguish the logic valuesof the memory element. Specifically, an amorphous state exhibits arelatively high resistance, and a crystalline state exhibits arelatively low resistance.

A conventional phase change memory element 1, illustrated in FIGS. 1Aand 1B, has a layer of phase change material 8 between first and secondelectrodes 2, 4, which are supported by a dielectric material 6. Thephase change material 8 is set to a particular resistance stateaccording to the amount of current applied between the first and secondelectrodes 2, 4. To obtain an amorphous state (FIG. 1B), a relativelyhigh write current pulse (a reset pulse) is applied through theconventional phase change memory element 1 to melt at least a portion 9of the phase change material 8 covering the first electrode 2 for afirst period of time. The current is removed and the phase changematerial 8 cools rapidly to a temperature below the crystallizationtemperature, which results in the portion 9 of the phase change material8 covering the first electrode 2 having the amorphous state. To obtain acrystalline state (FIG. 1A), a lower current write pulse (a set pulse)is applied to the conventional phase change memory element 1 for asecond period of time (typically longer in duration than thecrystallization time of amorphous phase change material) to heat theamorphous portion 9 of the phase change material 8 to a temperaturebelow its melting point, but above its crystallization temperature. Thiscauses the amorphous portion 9 of the phase change material 8 tore-crystallize to the crystalline state that is maintained once thecurrent is removed and the conventional phase change memory element 1 iscooled. The phase change memory element 1 is read by applying a readvoltage, which does not change the phase state of the phase changematerial 8.

One drawback of conventional phase change memory is the largeprogramming current needed to achieve the phase change. This requirementleads to large access transistor design to achieve adequate currentdrive. Another problem associated with the memory element 1, is poorreliability due to uncontrollable mixing of amorphous andpolycrystalline states at the edges of the programmable volume (i.e.,portion 9). Accordingly, it is desirable to have phase change memorydevices with reduced programming requirements and increased reliability.Additionally, since in the memory element 1, the phase change material 8is in direct contact with a large area of the first electrode 2, thereis a large heat loss resulting in a large reset current requirement.

Accordingly, alternative designs are needed to address the above notedproblems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate a conventional phase change memory element.

FIG. 2 illustrates partial cross-sectional view respectively of a phasechange memory device according to an embodiment of the invention.

FIGS. 3A-3D illustrate top-down views of the phase change memory deviceof FIG. 2 along the line 3-3′ according to embodiments of the invention.

FIGS. 4A-4D illustrate partial cross-sectional views of a method offabricating the phase change memory device of FIGS. 2A and 2B.

FIG. 5 is a partial cross-sectional view of the phase change memorydevice of FIG. 2 showing additional circuitry according to an embodimentof the invention.

FIG. 6 is a block diagram of a processor system having a memory deviceincorporating a phase change memory element constructed in accordancewith an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following detailed description, reference is made to variousembodiments of the invention. These embodiments are described withsufficient detail to enable those skilled in the art to practice them.It is to be understood that other embodiments may be employed, and thatvarious structural, logical and electrical changes may be made.

The term “substrate” used in the following description may include anysupporting structure including, but not limited to, a semiconductorsubstrate that has an exposed substrate surface. A semiconductorsubstrate should be understood to include silicon, silicon-on-insulator(SOI), silicon-on-sapphire (SOS), doped and undoped semiconductors,epitaxial layers of silicon supported by a base semiconductorfoundation, and other semiconductor structures, including those made ofsemiconductors other than silicon. When reference is made to asemiconductor substrate or wafer in the following description, previousprocess steps may have been utilized to form regions or junctions in orover the base semiconductor or foundation. The substrate also need notbe semiconductor-based, but may be any support structure suitable forsupporting an integrated circuit, including, but not limited to, metals,alloys, glasses, polymers, ceramics, and any other supportive materialsas is known in the art.

Embodiments of the invention provide phase change memory devices havingplanar memory elements. The embodiments are now explained with referenceto the figures, which illustrate embodiments and throughout which likereference numbers indicate like features. FIG. 2 illustrates across-sectional view of a portion of a phase change memory device 200constructed in accordance with embodiments of the invention. FIGS. 3A-3Dare top-down views of a portion of the memory device 200 along the line3-3′ according to the embodiments.

The memory device 200 includes memory elements 201, each for storing atleast one bit, i.e., logic 1 or 0. As described in more detail below,the memory elements 201 are planar and configured to have a reducedprogramming volume and/or programming voltage as compared to the memoryelement 1 (FIG. 1A).

Referring to FIG. 2, conductive plugs 14 are formed within a firstdielectric layer 20 and over a substrate 11. As shown in FIG. 5 anddescribed in more detail below, the substrate 11 can include additionaldevices and structures. Each memory element 201 is formed over and incommunication with a respective conductive plug 14. Each memory element201 includes a layer of phase change material 16 and self-aligned firstand second electrodes 31, 32. Each first electrode 31 is in contact witha respective conductive plug 14. Alternatively, more than one firstelectrode 31 can be in contact with a same conductive plug 14. Eachsecond electrode is in contact with a conductive interconnect 40, whichis connected to a second electrode select line 546 (FIG. 5).

In the memory elements 201, the first electrode 31 and second electrode32 are at opposing ends of the phase change material 16 at leastpartially along a same horizontal plane. Thus, the memory elements 201are planar. In the illustrated embodiment, the phase change materiallayer 16 is vertically disposed between second and third dielectriclayers 17, 18. The phase change material layer 16 and second and thirddielectric layers 17, 18 are arranged in a stack 211. The first andsecond electrodes 31, 32 are formed on sidewalls of the stack 211.

As shown in FIG. 3A, from a top-down perspective, the stack 211,including the phase change material layer 16, has a variable width(e.g., widths 316 a, 316 b) along the length 317 of the phase changematerial layer 16. For purposes of this specification, the length of thephase change material layer is measured along the distance between thefirst and second electrodes 31, 32 from the top-down perspective of FIG.3A. The width of the phase change material layer 16 is measured alongthe distance perpendicular to the length as indicated in FIG. 3A.

In the embodiment of FIG. 3A, the portions of the phase change materiallayer 16 adjacent the electrodes 31, 32 have a greater width 316 a thanthe width 316 b of a portion of the phase change material layer 16 at adistance between the electrodes 31, 32. The width of the phase changematerial layer 16 of FIG. 3A is shown progressively decreasing linearlyfrom each electrode 31, 32 to approximately the center 315 having width316 b. It should be understood that the narrowest portion of the phasechange material layer 16 need not be centered between the electrodes 31,32, but can instead be closer to one or the other of the electrodes 31,32.

FIGS. 3B-3D are top-down views of a portion of the memory device 200along the line 3-3′ according to other embodiments. As shown in FIG. 3B,the portion of the phase change material layer having a narrow width isextended as compared to that shown in FIG. 3A. Alternatively, as shownin FIGS. 3C and 3D, the width of the phase change material layerprogressively decreases in a step-wise manner from each electrode 31, 32to approximately the center 315 having width 316 b. Further, while thephase change material layer 16 is shown having a narrowest width at thecenter 315, the phase change material layer 16 can have a narrowestwidth at other points. Further other shapes, e.g., an hourglass shapeamong others, are possible such that the phase change material layer 16varies in width between the first and second electrodes 31, 32.

By providing a narrow width 316 b between the electrodes 31, 32, duringoperation, current crowding is induced and the programmable volume 16 acorresponds to a region of the phase change material layer 16 at andadjacent to the portion having the narrow width 316 b. This reduces heatloss through the electrodes 31, 32. This configuration enables betterscalability since the scale would not be limited by electrode 31, 32heat loss. The induced current crowding also enables a full reset stateof the programmable volume 16 a to improve the on/off resistance ratioof the element 201 and reduce the threshold voltage. Additionally, theprogrammable volume 16 a and programming voltages can be reduced ascompared to that in a conventional vertical memory element 1 (FIG. 1A).

The memory device 200 is operated to have two or more resistance states.This is accomplished by applying a reset current pulse to change theprogrammable volume 16 a of the phase change material 16 between thecrystalline and amorphous states. If, for example, three resistancestates are desired, the reset current is controlled to change a secondprogrammable volume 16 b between the crystalline and amorphous states.Additional resistance states are achieved by controlling the resetcurrent pulse to change additional programmable volumes between thecrystalline and amorphous states. Thus, the device 200 can be operatedsuch that the phase change material layers 16 of the elements 201 havemore than one programmable volume. Compared to multi-state programmingin conventional memory devices, the device 200 enables improvedstability, repeatability, reliability and consistency since theprogrammable volume 16 a can be provided at a distance from theelectrodes and the phase change can be complete.

Referring to FIGS. 2 and 3, each first electrode 31 is over and incontact with a respective conductive plug 14. Each second electrode isin contact with a conductive interconnect 40 formed in a fourthdielectric layer 21. As depicted in FIG. 2, the conductive interconnect40 is formed between and self-aligned to the second electrodes 32 ofadjacent memory elements 201.

FIGS. 4A-4D illustrate one embodiment of fabricating the phase changememory device 200 illustrated in FIGS. 2-3D. No particular order isrequired for any of the actions described herein, except for thoselogically requiring the results of prior actions. Accordingly, while theactions below are described as being performed in a specific order, theorder can be altered if desired.

As shown in FIG. 4A a first dielectric layer 20 is formed over asubstrate 11. The first dielectric layer 20 is etched to create vias 424within which conductive plugs 14 are formed. The conductive plugs 14 areformed of any suitable conductive material, such as titanium-nitride(TiN), titanium-aluminum-nitride (TiAlN), titanium-tungsten (TiW),platinum (Pt) or tungsten (W), among others.

As depicted in FIG. 4B, a second insulating layer 17, a phase changematerial layer 16 and a third insulating layer 18 are deposited over theconductive plugs 14 and the first insulating layer 20. The layers 16,17, 18 are formed as blanket layers. The programmable volume 316 (FIGS.3A-3D) is adjusted by adjusting the thickness of the phase changematerial layer 16.

In the illustrated embodiment, the phase change material 16 is achalcogenide material, for example, germanium-antimony-telluride and hasa thickness of, for example, about 100 Å. The phase change materials canalso be or include other phase change materials, for example, In—Se,Sb2Te3, GaSb, InSb, As—Te, Al—Te, GeTe, Te—Ge—As, In—Sb—Te, Te—Sn—Se,Ge—Se—Ga, Bi—Se—Sb, Ga—Se—Te, Sn—Sb—Te, In—Sb—Ge, Te—Ge—Sb—S,Te—Ge—Sn—O, Te—Ge—Sn—Au, Pd—Te—Ge—Sn, In—Se—Ti—Co, Ge—Sb—Te—Pd,Ge—Sb—Te—Co, Sb—Te—Bi—Se, Ag—In—Sb—Te, Ge—Sb—Se—Te, Ge—Sn—Sb—Te,Ge—Te—Sn—Ni, Ge—Te—Sn—Pd, and Ge—Te—Sn—Pt.

FIG. 4C illustrates the patterning and etching of the layers 16, 17, 18into stacks 211 for individual memory elements 201. Also, a conformalconductive layer is formed over the stacks 211. A spacer etch isperformed to form the self-aligned electrodes 31, 32 as sidewalls on thestacks 211. The electrodes 31, 32 are formed of any suitable conductivematerial, such as titanium-nitride (TiN), among others. The stacks 211are each formed partially overlying a respective conductive plug, suchthat when the first electrodes 31 are formed on a sidewall of the stacks211, the first electrodes 31 are in contact with a respective conductiveplug 14.

The stacks 211 are further patterned and a dry etch step is conducted toshape the stacks, including the phase change material layer 16 to have ashape shown in one of FIGS. 3A-3D or as desired and in accordance withthe invention.

As shown in FIG. 4D, a fourth dielectric layer 21 is formed over thestacks 211 and electrodes 31, 32. A via 440 is formed in the fourthdielectric layer 21 to expose the second electrodes 32 of adjacentmemory elements 201. To achieve the structure shown in FIG. 2, aconductive material is deposited within the via 440 self-aligned to andin contact with the second electrodes 32.

Additional structures can be formed to complete the memory device 200.For example, bit line 544, word lines 541, second electrode select line546 and conductive interconnects 542, as shown and described below inconnection with FIG. 5.

FIG. 5 is a partial cross-sectional view of the phase change memorydevice of FIG. 2 showing additional circuitry according to an embodimentof the invention. The memory elements 201 overlie bit line 544, wordlines 541 and conductive interconnects 542, which are supported bysubstrate 10. Isolation regions 550 within the substrate 10 isolate thevarious elements of the memory device 200. The structure shown in FIG. 5is only one example and other circuit designs including one or morememory elements 201 and/or the memory device 200 according toembodiments of the invention are contemplated as within the scope of theinvention.

FIG. 6 illustrates a simplified processor system 600 which includes amemory circuit 626 having a phase change memory device 200 constructedin accordance with the invention.

The FIG. 6 processor system 600, which can be any system including oneor more processors, for example, a computer, PDA, phone or other controlsystem, generally comprises a central processing unit (CPU) 622, such asa microprocessor, a digital signal processor, or other programmabledigital logic devices, which communicates with an input/output (I/O)device 625 over a bus 621. The memory circuit 626 communicates with theCPU 622 over bus 621 typically through a memory controller. The memorycircuit 626 includes the memory device 200 (FIGS. 2-3). Alternatively,the memory circuit 626 can include one or more of the memory elements201.

In the case of a computer system, the processor system 600 may includeperipheral devices such as a compact disc (CD) ROM drive 623 and harddrive 624, which also communicate with CPU 622 over the bus 621. Ifdesired, the memory circuit 626 may be combined with the processor, forexample CPU 622, in a single integrated circuit.

The above description and drawings are only to be consideredillustrative of specific embodiments, which achieve the features andadvantages described herein. Modification and substitutions to specificprocess conditions and structures can be made. Accordingly, theembodiments of the invention are not to be considered as being limitedby the foregoing description and drawings, but is only limited by thescope of the appended claims.

1-25. (canceled)
 26. A method of forming a memory element, the methodcomprising: forming a first electrode; forming a second electrode; andforming at least one layer of phase change material between the firstand second electrodes such that a programmable volume of the phasechange material layer is spaced apart from the first and secondelectrodes.
 27. The method of claim 26, wherein the first electrode,second electrode and phase change material layer are formed at leastpartially along a same horizontal plane
 28. The method of claim 27,wherein the configuring step comprises etching a first portion of thephase change material to have a first width less than a width of thesecond portion of the phase change material layer.
 29. The method ofclaim 28, wherein the first portion is approximately centered betweenthe first and second electrodes.
 30. The method of claim 27, whereinconfiguring step comprises etching the phase change material layer suchthat a width of the phase change material layer progressively decreasesfrom points adjacent to the first and second electrodes to a pointbetween the first and second electrodes.
 31. A method of forming amemory device, the method comprising: forming a first dielectric layer;forming a layer of phase change material layer over the first dielectriclayer; forming a second dielectric layer over the phase change materiallayer; forming a plurality of stacks by etching the first dielectriclayer, the second dielectric layer and the phase change material layer,each stacks formed having sidewalls, the sidewalls including edges ofthe phase change material layer; forming a first electrode on a firstsidewall of each stack and in contact with a first edge of the phasechange material layer; forming a second electrode on a second sidewallof each stack and in contact with a second edge of the phase changematerial layer, the first sidewall being opposite the second sidewall;and subsequent to forming the plurality of stacks, etching the phasechange material layer of each stack such that, for each stack, a firstportion of the phase change material layer has a first width less than awidth of the second portion of the phase change material layer.
 32. Themethod of claim 31, wherein the first portion is formed spaced apartfrom the first electrode.
 33. The method of claim 31, wherein the firstportion is formed spaced apart from the second electrode.
 34. The methodof claim 31, wherein the first portion is formed approximately centeredbetween the first and second electrodes.
 35. The method of claim 31,wherein the phase change material layer is etched such that a width ofthe phase change material layer progressively decreases from pointsadjacent to the first and second electrodes to the first portion. 36.The method of claim 31, wherein the phase change material layer isetched such that a width of the phase change material layer decreases ina step-wise manner from points adjacent to the first and secondelectrodes to the first portion.
 37. The method of claim 31, wherein thephase change material layer is etched such that a width of the phasechange material layer decreases linearly from points adjacent to thefirst and second electrodes to the first portion.
 38. The method ofclaim 31, further comprising forming a plurality of conductive plugs,wherein each first electrode is formed in contact with a respectiveconductive plug.
 39. The method of claim 31, further comprising: forminga third dielectric layer over the stacks, first electrodes and secondelectrodes; etching a via to expose two adjacent second electrodes; andfilling the via with a conductive material.